perf thread-stack: Eliminate code duplicating thread_stack__pop_ks()

Use new function thread_stack__pop_ks() in place of equivalent code.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20190619064429.14940-3-adrian.hunter@intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>